Vise structure for positioning an maintanining parts to be machined

ABSTRACT

The invention concerns a vise structure for maintaining parts to be machined, in particular but not exclusively for a micro-milling operation in a fast prototyping process. The invention is characterised in that it consists of a fixing plate ( 1 ) provided with reserves suitably distributed wherein is arranged a thermofusible material capable of being reversibly brought from liquid state to solid state whereof the free surface is urged continuously from the surface of said plate, the latter comprising means for heating/cooling ( 3, 4 ) said thermofusible material enabling to release/retain the part arranged on said plate.

[0001] The subject of the present invention is a novel vise structure for positioning and holding parts that need to be held in position, for example for a machining operation, particularly but nonlimitingly a micromilling operation in the context of a rapid prototyping process.

[0002] It must be understood that the invention is not restricted to this strict application but that, very much on the contrary, it can be implemented in any mechanical, laser, water jet, etc. machining process involving the temporary holding in position of the workpiece, in a nondestructive manner.

[0003] By extension, it can be implemented for any reversible holding in position, that can be used in a manufacturing or assembly process.

[0004] In general, reference will be made in the context of this application to the rapid prototyping process known by the name of STRATOCONCEPTION (registered trade mark) covered, in particular, by European patent EP 0 585 502-B1 of which the applicant of this application is proprietor.

[0005] Reference will also be made to French patent applications 98 14687 and 98 14688 of which the applicant of this application is also the proprietor.

[0006] It will be recalled that the general STRATOCONCEPTION process consists in a process of producing mechanical parts and items, particularly prototypes, from a specific computer-aided design of the type comprising the successive phases of:

[0007] virtual breakdown into elementary laminates;

[0008] placement as a panoply;

[0009] manufacturing parts in elementary laminates or layers;

[0010] rebuilding all the layers;

[0011] assembling the layers said laminates originating from a prior break-down of the part on predetermined planes and in one or more determined step(s).

[0012] The underlying principle consists in breaking down the volume that is to be reproduced in the form of a prototype into a multitude of laminates, produced by machining, for example rapid micromilling of a material in plate or sheet form, it being possible for example for said material to be made of wood, composite, plastic or metal.

[0013] The laminate that is to be machined can be held in place in several ways.

[0014] Thus, mechanical means operating on vacuum or alternatively the freezing of a thin film of water or the use of a sticky tape have been proposed and used.

[0015] While, in most cases, these means are satisfactory, they are not truly universal particularly for small and/or perforated parts. In the context of mechanical holding it is also necessary to carry out handling operations which are prejudicial to the economy of the process.

[0016] Furthermore, the processing in its current implementation entails the use of expensive consumable materials.

[0017] In addition, during some machining operations, problems associated with overthicknesses of the holding material are encountered.

[0018] Finally, the problem of cleaning the parts has not been satisfactorily solved.

[0019] There is therefore a need for a vise device which does not have the drawbacks of the devices of the prior art.

[0020] According to the invention, this result is achieved with a novel vise structure for holding parts that are to undergo a machining operation, particularly but nonlimitingly a micromilling operation in the context of a rapid prototyping process, characterized in that it consists in a fixing bed with suitably distributed reservations in which there is a thermofusible material which can be brought reversibly from the liquid state into the solid state, the free surface of which comes into continuity with the surface of said bed, the latter comprising means of heating/cooling said thermofusible material to allow the part arranged on said bed to be released/immobilized.

[0021] The invention will be better understood with the aid of the description given hereinafter with reference to the appended drawings in which:

[0022]FIG. 1 is a schematic sectioned view of a fixing bed according to the invention, in the rest position,

[0023]FIG. 2 is a schematic sectioned view of a fixing bed according to the invention in the phase of positioning the plate that is to be machined,

[0024]FIG. 3 is a schematic sectioned view of a fixing bed according to the invention, in the position of immobilizing the plate that is to be machined in position,

[0025]FIG. 4 is a schematic sectioned view of a fixing bed according to the invention in the position of holding the plate in position by actuating the vise,

[0026]FIG. 5 is a schematic sectioned view of a fixing bed according to the invention in the position of machining the laminate immobilized on the vise;

[0027]FIG. 6 illustrates an alternative form of embodiment of the device in FIG. 5, with further operation on the machined plate which has penetrating regions.

[0028] Reference will be made first of all to FIG. 1.

[0029] The bed-vise device generally referenced (1) according to the invention essentially comprises:

[0030] a tank (2) of fusible material,

[0031] a cooling circuit (3),

[0032] an array of resistive heating elements (4),

[0033] an open upper reservation (5) intended to receive fusible material from the tank (2) to which it is connected by a network of ducts (6).

[0034] The tank of fusible material forming a reservoir (2) comprises, in its side walls, resistive heating elements (7). The fusible material is displaced by an elastic air reservoir (8).

[0035] It will be understood that, when the fusible material is in the liquid state, pressurizing the reservoir (8) will increase its volume and therefore drive the fusible material through the ducts (6) toward the reservation (5).

[0036] In the depiction of FIG. 2, a plate (9) has been placed on the bed (1).

[0037] The format of the plate is slightly greater than the working area of the reservation (5). As the top face of the bed has been manufactured such that it is perfectly flat, it acts as a placement reference for setting down the plate that is to be machined or workpiece.

[0038] In the step depicted in FIG. 3, a retractable upper platen (10), mounted on a ball joint (11) keeps the plate in contact with the placement reference (the top surface of the bed) during the operation of sticking the plate down.

[0039]FIG. 4 illustrates the operational phase of operation of the vise.

[0040] A force represented by the arrow F is applied to the platen (10).

[0041] Air pressure represented by an arrow f is applied to the reservoir. It will be understood that F has to be greater than the opposite force created by f.

[0042] The fusible material is brought into its “liquid” phase by the resistive heating elements. By inflating the elastic reservoir, the fusible material fills the pocket under the plate. While maintaining the pressure in the elastic reservoir, the fusible material is cooled, the pressure in the elastic reservoir is shut off and the upper platen is retracted to allow machining to be performed.

[0043] Vents may be made in the bed (1) to serve as indicators that the cavity (5) has been filled.

[0044]FIG. 5 illustrates the machining of a plate (9) which, after machining, forms the actual laminate (12).

[0045] Machining is performed by implementing, for example, the stratoconception process.

[0046] The laminate is held uniformly. The milling cutter is able to machine into the thermofusible material without damage in order either to alleviate the effect of poor heightwise adjustment or to alleviate the problem of burrs left by the radius at the tip of the tool.

[0047] To release the laminate, the thermofusible material is brought into its “liquid” phase; excess on the laminate is eliminated by applying a solvent.

[0048] Volumes (13, 13′) hollowed away by milling and converted into chips have been depicted.

[0049] In the alternative form of embodiment of FIG. 6, the upper platen (10) is equipped with a cooling circuit (14).

[0050] The operating procedure may then be as follows.

[0051] The upper platen is once again applied to the machined plate. It is equipped with a cooling circuit. By heating the thermofusible material this material, under the effect of the increase in volume of the elastic reservoir, fills the volume left by the removal of the chips.

[0052] By adjusting the temperature gradient, the plate can be built up: the top platen rapidly cools the volume of material occupying the space left by the removed chips. The plate at this stage consists of two materials. There are then two alternatives:

[0053] either the upper platen is covered with a non-stick film (for example PTFE) and the plate can simply be removed and turned over by hand,

[0054] or the plate is connected by the thermofusible material to the top platen which retracts and becomes the new machining bed.

[0055] Very many variations can be made without departing from the scope of the invention. Note will also be taken of the following general comments:

[0056] the principle consists in using a plastic of any type, the nature of which is that it is thermofusible, allowing it, as a function of its temperature, to change from a liquid state to a solid state and vice versa several times;

[0057] the bed or platen may be made of metal or plastic;

[0058] secondary bearing surfaces able to act as reference blocks and to guarantee better distribution and better flatness of the bearing may be arranged in the reservation (5); the blocks also belong to the placement reference consisting of the upper face of the bed;

[0059] the thermofusible material will be chosen so that it avoids any chemical intervention with the plate that is to be secured;

[0060] the thermofusible material and its waste may, if necessary, easily be removed from the surface by any suitable process such a diluent, a solvent, a mechanical process, these being mentioned nonlimitingly;

[0061] the cooling passages may also be used if need be as heating passages;

[0062] according to a simplified alternative form of embodiment, the plastic may be supplied directly from above, without the device for injecting from the reservoir (2). In this case, a slight excess of fusible material is needed. It will be removed through lateral vents during the positioning, which may be done by hand, of the part (9). The system for cooling/heating the cavity (5) remains the same. 

1. A vise structure for holding parts that are to undergo a machining operation, particularly but nonlimitingly a micromilling operation in the context of a rapid prototyping process, characterized in that it consists in a fixing bed (1) with suitably distributed reservations in which there is a thermofusible material which can be brought reversibly from the liquid state into the solid state, the free surface of which comes into continuity with the surface of said bed, the latter comprising means (3, 4) of heating/cooling said thermofusible material to allow the part arranged on said bed to be released/immobilized, the said structure essentially comprising: a tank (2) of fusible material, a cooling circuit (3), an array of resistive heating elements (4), an open upper reservation (5) intended to receive fusible material from the tank (2) to which it is connected by a network of ducts (6), the said tank comprising, in its side walls, resistive heating elements (7).
 2. The vise structure as claimed in claim 1, characterized in that the fusible material is displaced by an elastic air reservoir (8).
 3. The vise structure as claimed in any one of claims 1 and 2, characterized in that it comprises a plate (9) arranged on the bed (1), of a format slightly larger than the working area of the reservation (5).
 4. The vise structure as claimed in claim 3, characterized in that a retractable upper platen (10), mounted on a ball joint (11) keeps the plate in contact with the placement reference during the operation of sticking the plate down.
 5. The vise structure as claimed in claim 4, characterized in that the bed (10) is equipped with a cooling circuit (14). 